import java.util.LinkedList;

/*
 * @lc app=leetcode.cn id=415 lang=java
 *
 * [415] 字符串相加
 *
 * https://leetcode.cn/problems/add-strings/description/
 *
 * algorithms
 * Easy (55.02%)
 * Likes:    632
 * Dislikes: 0
 * Total Accepted:    236.6K
 * Total Submissions: 430.1K
 * Testcase Example:  '"11"\n"123"'
 *
 * 给定两个字符串形式的非负整数 num1 和num2 ，计算它们的和并同样以字符串形式返回。
 * 
 * 你不能使用任何內建的用于处理大整数的库（比如 BigInteger）， 也不能直接将输入的字符串转换为整数形式。
 * 
 * 
 * 
 * 示例 1：
 * 
 * 
 * 输入：num1 = "11", num2 = "123"
 * 输出："134"
 * 
 * 
 * 示例 2：
 * 
 * 
 * 输入：num1 = "456", num2 = "77"
 * 输出："533"
 * 
 * 
 * 示例 3：
 * 
 * 
 * 输入：num1 = "0", num2 = "0"
 * 输出："0"
 * 
 * 
 * 
 * 
 * 
 * 
 * 提示：
 * 
 * 
 * 1 <= num1.length, num2.length <= 10^4
 * num1 和num2 都只包含数字 0-9
 * num1 和num2 都不包含任何前导零
 * 
 * 
 */

// @lc code=start
class Solution {
    public String addStrings(String num1, String num2) {
        // char[] data1=num1.toCharArray();
        // char[] data2=num2.toCharArray();
        LinkedList<Integer> linkedList1=new LinkedList<>(),linkedList2=new LinkedList<>();
        for (Character character : num1.toCharArray()) {
            linkedList1.addLast(character-'0');
        }
        for (Character character : num2.toCharArray()) {
            linkedList2.addLast(character-'0');
        }
        StringBuilder stringBuilder=new StringBuilder();
        int middle=0;
        while (!linkedList1.isEmpty() && !linkedList2.isEmpty()) {
            int number1=linkedList1.pollLast();
            int number2=linkedList2.pollLast();
            middle+=number1+number2;
            stringBuilder.append(middle%10);
            middle/=10;
        }
        while (!linkedList1.isEmpty()) {
            int number1=linkedList1.pollLast();
            middle+=number1;
            stringBuilder.append(middle%10);
            middle/=10;
        }
        while (!linkedList2.isEmpty()) {
            int number2=linkedList2.pollLast();
            middle+=number2;
            stringBuilder.append(middle%10);
            middle/=10;
        }
        if (middle!=0) {
            stringBuilder.append(middle);
        }
        return stringBuilder.reverse().toString();

    }
}
// @lc code=end

